This invention constitutes a significant improvement in diluting and dispensing devices used primarily for preparing samples in clinical laboratories, industrial laboratories, or anywhere that precision fluid measurement and delivery is required. Heretofore, commercially available reagent containing diluting devices have required separate reagent reservoirs, but normally feed a reagent pump through a valve or other sealing means. The valve opens to a separate reagent reservoir allowing the reagent pump, normally a syringe, to cycle and fill with reagent. The valve then rotates to its discharge postion and the pump discharges the reagent, along with the sample picked up separately if in a sample dilution mode. Discharge is normally through a tube into the test receptacle.
New technology diluters having advanced electronics and programming capabilities have recently been marketed but have remained tied with old pumping technology using valves and separate reservoirs. This use of old pumping technology imposes a severe penalty on these new units whose great flexibility in programming is thus not truly realized because the operator is limited to the reagent that is already in the system. Changeover to a new reagent requires considerable time and effort to clean out all the components in contact with the old reagent including the reservoir, valves, pumps and the like. The valve itself is, of course, a source of contamination, is usually a high maintenance item, and one result is inaccuracies in measurement. Open reagent reservoirs are also subject to contamination.
Some of the prior art includes dispensing devices having a removable, single cylinder, liquid filled syringe as illustrated by Glenn, U.S. Pat. No. 4,155,490, and Downings, et al., U.S. Pat. No. 3,931,915. Since the foregoing are limited to one large reagent piston, they are normally not satisfactory for operation at sample volumes at the low end of the scale, i.e. 2 to 5 microliters. Such devices probably have lower limits in the 50 microliter range. Therefore, Glenn and Downings, et al. must be considered as usable primarily for dispensing of reagents only. Another reference, Chen, U.S. Pat. No. 3,982 667, shows a removable reagent syringe diluter with concentric sample and reagent pistons whereby the sample piston actually passes through a seal in the reagent piston. Chen's approach utilizes the same concept of a single piston cylinder as does Glenn and Downings, et al., but Chen does teach the ability to work with small sample sizes since the disclosure includes a separate small sample piston. One disadvantage of Chen is that movement of the sample piston can dislodge the reagent piston, thereby causing significant volumetric errors in the sample size, and some error in reagent size. A further disadvantage is that a significant volume of reagent is unusable as the reagent piston must stop somewhat short of its cylinder upper end if the sample piston is to function along its full stroke. One more disadvantage is that there are limitations on the diameter of the reagent piston as a consequence of the geometry of the sample piston and its seals. Moreover, the Chen concept appears costly to manufacture and maintain by reason of its complexity. Moreover, Glenn, Downings, et al., and Chen all teach cylinder fastening systems that are manual, requiring some operator dexterity, as opposed to the automatic cartridge attachment means of the present invention.
The present invention offers all of the flexibility of programmable dilutors and dispensers combined with readily removable and storable, extreme accuracy, low cost, simple, fluid cartridges. In the preferred embodiment, a drive motor actually disconnects the cartridge automatically upon command to further simplify operation. In addition, a simple single piston version is offered, primarily for dispensing reagents, which also utilizes the novel automatic cylinder attachment means of the present invention. Accordingly, the present invention offers substantial unique advantages over the prior art that are extremely valuable to the end user or operator. These advantages are described in significant detail in the following section.